Two ways to pay for throughput
DynamoDB charges for reads and writes using capacity units, and you pick how that capacity is supplied.
Provisioned mode
You declare how many Read Capacity Units (RCU) and Write Capacity Units (WCU) the table can use per second.
- One RCU is one strongly consistent read per second for an item up to 4 KB.
- One WCU is one write per second for an item up to 1 KB.
- Auto scaling can raise and lower the provisioned numbers based on utilization.
- Best for predictable, steady traffic where you optimize cost.
On demand mode
You pay per request with no capacity planning. The table scales instantly to traffic.
- No throttling from under provisioning, ideal for spiky or unknown workloads.
- Generally costs more per request than well tuned provisioned capacity.
Throttling and bursts
If requests exceed available capacity in provisioned mode, they are throttled. A small amount of unused capacity is saved as burst capacity to absorb short spikes.
Diagram
Key idea
Use provisioned capacity for steady predictable load to control cost, and on demand for spiky or unpredictable traffic where simplicity matters.